1. Field of the Invention
The present invention relates to a dispersing apparatus for dispersing in a finely granulated form a liquid blend which contains solid matters such as paints, inks and like pigments, as well as a resin varnish, a solvent and additives (as required).
2. Description of the Prior Art
In a conventional dispersing apparatus of this type as shown in, for example, FIG. 1, an apparatus body 10 is provided on a cylinder 53 of an elevator device 50, such as a hydraulic cylinder that moves up and down, and primary vanes 14 are provided at the end of a main shaft 12 that is rotated via a V-belt or the like means by a motor 41 which is installed in the apparatus body 10. The primary vanes 14 are allowed to rotate in a basket 20 that is firmly fastened to the lower side of the apparatus body 10 by rods 13 and that is disposed nearly at the center of a tank 60 so as to disperse a liquid blend 65 that contains solid matters such as paints, inks and like pigments. The basket 20 contains dispersing media 37 such as glass balls, steel balls, ceramic balls and zirconia balls.
The tank 60 has a drain valve 61 provided in a side wall which is continuous to the bottom wall of the vessel, and further has wheels 62 provided on the lower surface of the bottom wall, so that it can be moved.
Moreover, a sub-shaft 46 is driven being directly coupled to a motor 48 and moves up and down together with the apparatus body 10. Secondary vanes 47 are attached to an end of the sub-shaft 46, and is located at a lower portion in the tank 60 outside the basket 20 being spaced apart therefrom.
The basket 20 has numerous pores formed in the side walls thereof. The pores are formed by using a mesh-like wire gauze having a number of fine holes or slits perforated therein.
The basket has in the upper surface thereof an opening at a central portion in which the main shaft will be inserted and through which will be introduced the liquid blend that contains solid matters such as paints, inks and like pigments inside the tank. The basket further has a top cover that is fastened to the top flange thereof, the top cover being made of a thin metal plate having an upper guide surface for preventing the dispersing media from escaping and for guiding the blend into the opening.
In general, pigments that are placed in the market are aggregated and are forming Secondary grains (primary grains of the pigment are usually smaller than 1 micron). When used in their own forms, therefore, the pigments precipitate and are separated while the paint is being preserved. Even when the pigments are stirred, the obtained coated film is not beautifully finished due to aggregates of secondary grains. To overcome this problem, in general, the liquid blend containing solid matters such as pigments, a resin varnish, a solvent and additives (used as required), is dispersed and is finely granulated through the steps of premixing and dispersion.
In the premixing, the varnish and the pigment are mixed together, and the secondary grains of the pigment are wet with the varnish to form a paste thereof, which facilitates the subsequent step of dispersion.
In the conventional premixing method, the resin, solvent and the like are thrown into the tank 60 to about one-third the depth of the tank 60 at a place other than the place where the dispersing apparatus is placed, and the pigment is then thrown therein. The mixture is then premixed using a mixer (e.g., a simply constructed mixer by attaching vanes to the end of a long shaft coupled to a motor) to obtain a paste-like mixture thereof. After the pigment is thrown in a whole amount into the tank 60, a solvent and the like are then thrown therein to dilute the mixture.
In the following step of dispersion, the tank 60 is moved to the place where the dispersing apparatus exists, the elevator device 50 is operated to lower the device body 10, and the basket 20 and the secondary vanes 47 are submerged in the blend 65 in the tank 60. As the motor 41 and the motor 48 are driven to rotate the primary vanes 14 the secondary vanes 47, large grains in the blend 65 in the basket 20 are finely dispersed due to shearing stress between the dispersing media 37 and the blend in the basket 20, whereby finely dispersed grains flow out through pores, mesh or slits in the side walls of the basket 20, undergo convection in the tank 60, flow again into the basket 20 from the upper direction, and are dispersed more finely (for example, see Japanese Patent KOKAI NOs. S60-122033, S61-293536 and H3-72932).
The conventional dispersing apparatuses, however, leave the below-mentioned problems unsolved.
(1) To carry out the steps of premixing and dispersion using the conventional dispersing apparatus, the tank 60 must be installed on the dispersing apparatus after the basket 20 and the secondary vanes 47 are raised. Under this condition, a blend of resin, solvent, pigment, etc. is thrown into the tank 60. The basket 20 and the secondary vanes 47 are then lowered to premix the blend by the secondary vanes 47. That is, the secondary vanes 47 are located near the inner peripheral wall of the tank 60, and the blend in the tank 60 is not stirred to a sufficient degree.
(2) In the premixing step, the pigment is thrown little by little into the mixture of the resin and the solvent that is being stirred by the secondary vanes 47 to accomplish better stirring efficiency. Because of the reason mentioned in (1) above, however, the basket 20 and the secondary vanes 47 are lowered after the blend of resin, solvent and pigment is thrown in, and the premixing is effected by the secondary vanes 47 or the pigment is thrown in little by little while frequently ascending and descending the secondary vanes 47, resulting in a poor production efficiency.
(3) Because of the reasons mentioned in (1) and (2), therefore, the blend must be thrown into the tank 60 and must be premixed in another place arousing, however, the following problems.
(3-1) A place is required for placing the tank 60 for premixing.
(3-2) Premixing efficiency is poor since the premixing is carried out using a simply constructed mixer. A large mixing device for improving premixing efficiency requires an increased cost for facilities, as a matter of course.
(3-3) After the premixing, manpower and time are required for moving the tank 60 to the dispersing apparatus.
(3-4) With the movable tank 60 equipped with wheels, limitation is imposed on the capacity thereof, i.e., from 500 to 1000 liters, making it difficult to construct the tank 60 in a large size. This makes it impossible to batchwisely process the blend in large amounts.
(4) To disperse many kinds of paints in succession, attention must be given so that the paints are not mixed into each other. Therefore, the tank 60, the members such as basket 20 and secondary vanes 47 in the dispersing apparatus, must be completely washed after one paint is dispersed but before starting the dispersion processing of another paint. In the conventional dispersing apparatus, however, the tank 60 is washed after moved to another place from the dispersing apparatus, and the members such as the basket 20 and the secondary vanes 47 of the dispersing apparatus must, on the other hand, be washed by moving the washing tank to the dispersing apparatus. Thus, cumbersome work is required for the washing operation.
(5) Furthermore, since the guide surface is formed only at a central portion of the top cover at a very shallow angle, the liquid blend containing solid matters such as paints, inks and like pigments in the tank is guided into the basket at a poor efficiency. Besides, dispersion media such as glass balls, steel balls and ceramic balls that fly beyond the top cover through the opening are not recovered into the basket but fall on the tank. Therefore, the dispersion efficiency in the basket is not improved.
(6) Among the solid grains dispersed in the basket 20, those grains larger than the width of the slits are not permitted to pass through the slits and stay inside the basket 20 so as to be further finely dispersed. However, the solid grains of sizes close to the width of the slit may often stick in the slits, causing the slits to be partly clogged and the dispersion efficiency to be decreased.
(7) Laborious work is required for washing the solid matters stuck in the slits.